Soapmaking process



Nov 2, 1 48 G. BBRADSHAW 2,452,72

SOAP-MAKING PROCESS Filed June 29, 1945 George B firm/shah INVENT R.

Arum/m Patented Nov. 2, 1948 UNITED STATES PATENT OFFICE SOAPMAKINGPROCESS George B. Bradshaw, Wilmington, Del.

Application June 29, 1945, Serial N0. 602,227

4 Claims.

This invention relates to the manufacture of soap. More particularly,this invention deals with that process of making soap wherein naturalfats, consisting essentially of glycerine esters of higher fatty acids,are first converted into lower alkyl esters of said higher fatty acids,say the methyl, ethyl, propyl or butyl esters, and the latter are thensaponified with caustic alkali, liberating respectively methyl, ethyl,propyl, or butyl alcohol.

According to my invention fatty materials, predominantly lower alkylesters of fatty acids, are continuously saponified at a temperature ofabout 105 C. under agitation and pressure and, after reducing the vaporpressure by heat interchange and by addition of cold liquor, separatedinto neat soap and nigre under atmospheric pressure conditions.

The ordinary soap boiling process involving a recovery of glycerine anda purification of the soap by the separation of a neat soap and a nigreis an operation requiring 4 to 14 days and the consumption ofconsiderable energy in the form of steam. The saponification in itselfis an exothermic reaction. There is enough heat set free to bring thestarting materials to the reacting temperature. This could be an idealsituation for a continuous process heat exchange operation in which theheat of reaction would be used to heat the starting materials. Howeverthe diversity and number of time consuming steps in soap boiling ofglycerides prevent it from being amenable to such a ration-a1 process.In soap boiling the mass of material under treatment is agitated by livesteam while in a dispersible condition which is obtained by the presenceof enough electrolyte to produce a partial salting out or grainingeffect. The saponification and the removal of the glycerine occur instages generally involving delays for slow gravity separation of liquorfrom grained soap or curd. Finally the electrolyte concentration islowered by sedimentation with draining ofi of free liquor and byintroduction of water so that a portion of the soap, with the aid of theboiling employed, is dissolved. The soap is then allowed to stand withas little heat loss as possible until it separates into a neat soap anda nigre. The nigre contains most of the impurities. The neat soap has anespecial brightness not easily obtained by any other procedure, but itcontains about /2% salt.

The various difficulties just outlined which prevent using a rationalcontinuous process for saponification to produce neat soap are overcomeby my invention. The manufacture of soap from lower alkyl esters offatty acids instead of from glycerides requires no steps for removingglycerine. The previous removal of the glycerine has also removed mostof the impurities from the fat. However the lower alcohol will still bepresent. It is useful during the saponification because it increases thediffusivity and dispersivity of the charge. Practically no salt need bepresent. The alcohol, however, because of its low boiling point causesfoam which precludes saponification in an open boiling operation or aseparation in the manner of the previous art over a nigre.

According to my invention, the saponification, for example, of themethyl esters of fatty acids is carried out continuously under agitationand pressure, under such conditions that the mass is continuallyreactive and easily agitated and is fiowable. Also,'directly aftersaponification it can be fitted or finished by the continuous additionof water or very dilute electrolyte which at the same time brings thetemperature of the mass below the foaming point but not below a suitabletemperature for separation into neatsoap and nigre. Thus an entirely newresult is obtained, that is a separation of neat soap and nigre withouta previous boiling operation in the fitting step. The alcohol which hasacted as an adjuvant is removed in any subsequent drying operation.

An outline description of a soap production according to my inventionnow follows. The finished or fitted soap is discharged continuously fromthe last of a series of agitated closed reactors to heat insulatedsettling vessels where the soap can separate into two layers with atemperature loss of only 5 to C. After settling the bright upper layerof neat soap is drawn off and made into merchantable soap in one of theusual ways or as discussed later in this specification. The lower layeror nigre is grained, and settled. The lye containing methyl alcohol isdrained off and the soap fitted and allowed to separate to a neat soapand a second nigre. The nigre and lyes from this operation are worked upfore their values. The neat soap from this second nigre is boiled upwith about an equal weight of water or very dilute brine depending onconditions and fed continuously to the reactors in admixture with hotmethyl esters. These methyl esters have been heated to about C.preferably by heat interchange as a result of removing the heat ofreaction of the saponification. The esters may be the heat exchangemedium or be heated indirectly by the medium. It is only necessary thatunder the heat conditions existing the starting materials are hot enoughso that the reaction starts and ends quickly enough for the time ofpassage and that the reaction occurs between about to C. This hotmaterial is fed continuously seriatim to a series of, say-four, agitatedpressure reactors. At the same time the proportioned amount of causticsoda is fed to the reactors but distribul69 tively, in stages, that is,assuming the main reaction is carried out in three reactors, then aboutone third of the caustic soda is fed continuously to each reactor. Thetime of passage through the reactors is governed by the speed ofreaction and the emciency of the heat transfer. To the fourth or lastreactor is continuously added the amount of water or dilute electrolyteneeded 4 described above. The reactors were each of about 600 gallonscapacity. To start the operation the methyl esters were heated to 95 C.in the storage tank i and then flowed through the jackets of thereactors before being fed by pump 3. After starting they were keptheated to 95 C. by the heat taken up in passing through the jackets.

to fit the soap. This last addition can be such as to prepare the soapfor separation into neat soap v and nigre with about 88% of the totalsoap as neat soap. It also cools the mass to such a point that unduefoaming does not occuron discharge of the material to atmosphericpressure for the neat soap and nigre step.

A plant suitable for carrying out the previously described process isshown diagrammatically in the accompanying drawing. Referringto thedrawing, the tank I is the storage tank-for methyl esters Tank 2 isstorage for caustic soda solution. Feeder pumps 3, 4, and 5 are for hotmethyl esters, for hot diluted neat soap from nigre and for caustic sodasolution respectively. These pumps feed the materials continuously inproportioned amounts to the agitated pressure reactors 5, i, '3, and 9-.These reactors are connectedin series so that the discharge from thefirst feeds the second and so on. Preferably these machines areconstructed similarly to a standard jacketed soap crutcher with the feedinto the center draft tube except they are closed in for pressure work;The agitation forces the material down through the center draft tube andup the sides. The discharge outlet is at the top. The center tunnel ordraft tube is double walled and the machines are jacketed forcirculation of the heat. transfer medium. Between reactors 8 and S.

is a throttle 28 for maintaining the desired pressure in E5, 7 and 8.Insulated tanks capable each ofholding 24 hours production are 10 50 10E0 and H3 These can be of the usual type for soap boiling and separationinto neat soap and nigre. circulation of a heat transfer medium throughtheir-jackets preferably entering first the jackets of reactor 9. Thismedium afmr leaving the jackets of reactor 6 passes through coils in themethyl ester storage. tank I and then returns to jackets of reactor 9.Alternatively the methyl esters may be heated directly by passing fromtank I to the jackets of reactors 9, ll, 7, and 6 in series and then befed by pump 3 and pipe 52 to the series, of reactors commencing with 5.Caustic soda solution is fed through pipe 24, and

' partitioning valves 25, 26-, and 2'! to the feed Methyl esters,temperature'95 C. (2800 lbs.

fatty acids) 2940 Caustic soda, 45%, temp. 25 C. equals 6% excess 945Dilute neat soap from nigre, temp. 95" C. (contains 0.7% salt and 280lbs. fatty acids total) 900 5% salt solution, temp. 25 C 790 Thesematerials were treated in the apparatus Heat is removed'from thereactors by the.

Pounds The electrolyte solution fed continuously through pipe 23 toreactor 9 was a 5% salt solution. The strength of this solution and theamount used will vary with the fats employed and the percentage of thetotal fatty acids desired in the nigre. The control is well known tothose skilled in the art and is clearly explained for example in WignersManufacture of Soap. The amount can be varied by varying the dilution ofthe returned neat from nigre soap. Also the amount needed depends on theheat balance of the system. It is necessary to bring the temperattue ofthe fitted soap below the point at which it will foam out of thesettlers. In this case the material discharged from reactor 9 was at atemperature of C. and on standing 24 hours was found sepa rated to aneat soap and a nigre. The neat soap was 62.27% fatty acids andcontained 87.92% of the total fatty acids and the nigre 12.08%. Thenigre for each days run was grained by addition of brine in the usualway and fitted so that 24.73% of its fatty acids went to a second nigre.This 2 1.73 amounted to 92 pounds of each hours consumption of 2800 lbs.fatty acids or 3.3 The neat soapfrom the new' nigre was boiled up withan equal amount of 1% brine and returned at the rate of 900 lbs; dilutedhot material per hour. The percentage of salt in the material passingthrough the first three reactors was less than 0.15% but enough toguarantee the necessary fluidity. This means a soap exceedingly low insalt can be made if the original fitting is done with dilute causticsodasolution instead of brine. In such case the excess caustic in theneat soap can be neutralized in the crutchers ahead of the chillingrolls by addition f castor oil fatty acids or-methyl stearate or similarfatty material. In the saponification: just described the heat balancewas about as follows:

' Calories Heat from reaction,

29 10 1bs.=1333 kilos 75 100,000

The temperature in reactorsfi, i and 8 ran from about to C... Thepressure was maintained'equivalent to 115 C.

Example II. -An operation for about 8900 lbs. per hour of. neat soapmade from an 80 tallow 20% coconut oil composition is now described.

For a 24 hour operation 123,100 lbs. crude tallow containing 12%fattyacids' in. free-state was ester interchanged using a special acidcatalyst to produce 120,214 lbs. oil containing 86% methyl esters, 8%glycerides and 6% free fatty acids. 29,800 lbs. refined coconut oil alsowas ester interchanged but using an alkaline catalyst toTproduce 29,530lbs. oil containing 97 /2% methyl esters and 2 /2% glycerides. Thecombined esters totaling 149,744 lbs. had a saponification value of 204.The theoretical amount of caustic soda needed was 21,780 lbs. There wasused 51,500 lbs. of 45% solution that is 6% excess. The materialsconsumed each hour to feed the reactors were:

Pounds Methyl esters, temperature 95 C. (5,940 lbs.

fatty acids) ""6240 Caustic soda, 45% temp. 25 0. equals 6% excess 2146Diluted neat soap from nigre, temp. 95 C.

(594 fatty acids) 1815 5% salt solution, temp. 25 C 1420 There were fourreactors each of 1200 gallons capacity. The procedure was practicallythe same as in Example I. The neat soap was 62.35% fatty acids andcontained 86.8% of the total fatty acids in the operation for separationof neat soap and nigre. From the nigre not returned to the operation andother losses there was a total loss of 5.4% of the fats charged. Of thisloss 75% was recovered as fatty acids. There was about 0.17% salt in thematerial passing through the first three reactors. The averagetemperature of the first three reactors was 110 C.

Preferred procedures have been detailed. However it is understood thatthe invention includes variations within the scope of the claims whichfollow.

I claim:

'1. A process for making soap which comprises saponifying a mixture oflower alkyl esters of higher fatty acids and an aqueous soap solution byadding caustic alkali to said mixture in several successive stages attemperatures between about C. and about YC. under autogenous pressureand continued agitation, adding to the resulting, hot, saponificationproduct a cool, dilute, aqueous solution of an electrolyte, therebyreducing the temperature of the resultant mixture to about 85 C.,permitting said mixture to settle at atmospheric pressure, and thenseparating the neat soap from the nigre therein.

2. The process of claim 1 wherein the mixture obtained upon addition ofthe electrolyte solution to the saponification product contains about55% by weight of fatty acids combined in the form of soap.

3,. The process of claim l wherein the esters are preheated by heatexchange with the saponifying material.

4. The process of claim 1 wherein the soap solution is the neat soapobtained by fitting the nigre from the settling operation.

GEORGE B. BRADSHAW.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date Australia Feb. 18,1943 Australia Jan. 16, 1943 Number Number

